Design of SCALDO based high-current DC power supply

Abstract

Supercapacitor assisted (SCA) techniques are primarily based on supercapacitors having in the order of one million times more capacitance, together with one to two orders of magnitude smaller equivalent series resistance (ESR), compared with conventional capacitors. In the first successful SCA technique, the supercapacitor-assisted low dropout regulator (SCALDO) combined a linear regulator in series with a supercapacitor to act as a lossless voltage dropper. SCALDO created the opportunity to develop an entirely new family of highly efficient, interference-free, very-low-frequency DC-DC converters, which have evolved further into several branches over the last 6 years.

Leading data centre operators such as Google have announced their intention to move toward 48 V server rack architecture to minimise power losses in distribution lines and to improve overall operating efficiency. This thesis investigated the potential of the SCALDO technique to develop a high-current DC power supply suitable for Google server racks, meeting requirements such as electrical isolation, fast transient response, high efficiency and DC-UPS capability within the converter.

Work related to this thesis proved that by creatively extending the SCALDO technique to achieve higher current at high voltage and further developing a bulk DC-rail from AC input by extending the previously proven fast supercapacitor charger technique, a SCALDO-assisted high-current DC power supply can be achieved. As a proof-of-concept project with a DC output of 12 V (one fourth scale) at 10 A load current capability, several key circuit blocks were developed including: (i) high current discrete LDO of 10 A; (ii) four switch implementation of a SCALDO stage; and (iii) a transformer-isolated input DC stage to feed the output SCALDO stage based on a hybrid-type medium frequency switch mode. This overall implementation is expected to overcome the limitations of a direct-SCALDO stage, maintaining high end-to-end efficiency. Matlab and LTspice simulation models were developed to observe the behaviour of these new power converter techniques.

The thesis discusses the significance of this work, related techniques, the loss-circumventing principle in the RC charging loop, which is the theoretical basis of SCALDO, and the design and simulation details of a novel power conversion technology. It also presents the implementation details of the prototypes built to verify this approach.